Are you using TouchWiz or a 3rd party launcher? If it's a 3rd party launcher, there's usually an Edit choice if you long-press the icon (or blank space, in your case) and you can select an icon, of you can install a different icon set.

If the icon is showing in the app drwer, simply remove the "blank space" on the home screen, then drag the Contacts icon from th app drawer to the homecreen.